Trying to set custom drive icon in Finder appears as preview file icon

I'm trying to change the icon for my external HDD through Finder. However, when I copy the ".icns" file onto the Get Info window, it appears as the icon below (which is the Preview app icon on a piece of paper with "ICNS" underneath it). When I go to see the hidden files, it shows the .icns file I selected as the ".VolumeIcon.icns" file. Even after disconnecting the drive multiple times, it still does not show the icon in Finder. I heard it may be an ExFAT problem, but I am unsure. Any help appreciated.